1. Field of the Invention
This invention relates to a heat-resistant positive type photosensitive resin composition containing a polyimide precursor or a polyoxazole precursor having photosensitivity, a process for producing a pattern and electronic parts using the same.
2. Background Art
For a surface protective film or an interlaminar insulation film of a semiconductor device, a polyimide resin having excellent heat resistance, electric characteristics, mechanical characteristics, etc. has heretofore been used. However, whereas a semiconductor element has now been required to be highly integrated and large-sized in recent years, an encapsulating resin package is required to be thin and small-sized. Thus, a system such as a surface application by LOC (lead on chip) or solder reflow has been employed so that a polyimide resin excellent in mechanical characteristics, heat-resistance, etc. than before has been earnestly desired.
On the other hand, a photosensitive polyimide in which photosensitive characteristics are provided to the polyimide resin itself has been used. When this material is used, there are characteristics that pattern formation steps can be simplified and complicated preparation processes can be shortened.
A heat-resistant photoresist comprising a photosensitive polyimide or a precursor thereof and uses thereof have been well known in the art. For example, as a negative type material, there have been proposed a method of introducing a methacryloyl group into a polyimide precursor through an ester bond or an ionic bond (Japanese Provisional Patent Publications No. 115541/1974, No. 40922/1976, No. 145794/1979, No. 38038/1981, etc.), a soluble polyimide having a photopolymerizable olefin (Japanese Provisional Patent Publications No. 108031/1984, No. 220730/1984, No. 232122/1984, No. 6729/1985, No. 72925/1985, No. 57620/1986, etc.), a self-sensitization type polyimide having a benzophenone skeleton and an alkyl group at an ortho position of an aromatic ring to which a nitrogen atom is to be bonded (Japanese Provisional Patent Publications No. 219330/1984, No. 231533/1984, etc.), and the like.
In the above-mentioned negative type material, an organic solvent such as N-methylpyrrolidone, etc. is required at the time of development so that, in recent years, a positive type photosensitive resin which can be developed by an aqueous alkaline solution has now been proposed. As a positive type material, there have been proposed a method of introducing an o-nitrobenzyl group into a polyimide precursor through an ester bond (J. Macromol. Sci. Chem., A24, 12, 1407, 1987), a method of mixing a naphthoquinone azide compound with a soluble hydroxylimide or a polyoxazole precursor (Japanese Provisional Patent Publication No. 60630/1989, U.S. Pat. No. 4,395,482), a method of introducing a naphthoquinone diazide compound into a soluble polyimide through an ester bond (Macromolecules, 23,pp. 4796-4802, 1990), a chemical amplification type polyimide (Japanese Provisional Patent Publication No. 763/1995), a material in which naphthoquinone diazide is mixed with a polyimide precursor (Japanese Provisional Patent Publication No. 13315/1977), a method of using an acid generator with a polyamide acid ester or a polyamide phenol in which the phenolic hydroxyl group is protected by an alkoxycarbonyl group (Japanese Provisional Patent Publication No. 202489/1999), and the like.
However, in the above-mentioned negative type material, there are problems in their function or resolution, or depending on the uses, lowering in yield at production occurs. Also, in the above-mentioned materials, a structure of the polymer to be used is restricted so that physical properties of a film finally obtained are also restricted and they are not suitable for multi-purpose use. On the other hand, in the positive type materials, there are similar problems that sensitivity or resolution is low due to the problem accompanied by an absorption wavelength of a photosensitive agent as mentioned above, or its structure is restricted. Moreover, in the above mentioned materials, there are problems that a film thickness is decreased by a high temperature treatment after formation of an image or a pattern shape is deteriorated due to an effect of a basic component existing in air with a minute amount.
Also, there are materials in which a diazonaphthoquinone compound is mixed with a polybenzoxazole precursor (Japanese Patent Publication No. 46862/1989) or a phenolic hydroxyl group is introduced in place of a carboxylic acid such as those in which a phenol portion is introduced into a polyamic acid through an ester bond (Japanese Provisional Patent Publication No. 307393/1998), but these materials are insufficient in development and decrease in film thickness at an unexposed portion or peeling of a resin from a substrate occurs. Also, to improve developability or adhesive property of a material, a material in which a polyamic acid having a siloxane structure in the polymer skeleton has been proposed (Japanese Provisional Patent Publications No. 31861/1992 and No. 46345/1992), but it contains the polyamic acid so that preservation stability becomes poor as mentioned above. Also, these materials use diazoquinone compounds containing a number of aromatic rings as an acid generating agent so that there is a problem that mechanical properties after thermal curing are markedly decreased so that they cannot be used as a practically applicable material.
Thus, either of the materials cannot be practically used as of today.
The present invention is to provide a heat-resistant positive type photosensitive resin composition which can solve the above-mentioned problems possessed by the conventional photoresist, which can sufficiently endure even when a polyimide precursor or a polybenzoxazole precursor which provide photosensitivity has any structure, and has good sensitivity and resolution, and is less affected by a basic component existing in air with a minute amount, by formulating a compound which can induce an elimination reaction of a protective group in a polyimide precursor or a polybenzoxazole precursor in which an alkali-soluble group had been protected by an eliminatable group under acidic conditions by irradiating radiation to the polyimide precursor or the polybenzoxazole precursor.
Also, the present invention is to provide a process for producing a pattern which can give a pattern capable of being developed by an alkaline aqueous solution, excellent in sensitivity, resolution and heat-resistance, and a pattern having good shape can be obtained.
Also, the present invention is to provide electronic parts having high reliability by having a pattern with good shape and characteristics.
The present invention relates to the following.
1) A positive type photosensitive resin composition which comprises
(A) a polyimide precursor or a polyoxazole precursor having a group represented by xe2x80x94OR,
wherein R represents a monovalent group constituting a acetal or ketal, an alkoxyalkyl group or an alkylsilyl group, which can be converted into a hydrogen atom by decomposition with an action of an acid, in the molecule which is bonded to an aromatic ring, and
(B) a compound which generates an acid by irradiating radiation.
2) A positive type photosensitive resin composition as defined above, wherein the component (A) is a polyimide precursor having a structural unit represented by the formula (1): 
wherein R1 and R2 each independently represent a tetravalent organic group; each R3 independently represents a monovalent organic group; each R4 independently represents a monovalent group constituting acetal or ketal, an alkoxyalkyl group or an alkylsilyl group, which can be converted into a hydrogen atom by decomposition with an action of an acid.
3) A positive type photosensitive resin composition as defined above, wherein (B) the compound which generates an acid by irradiating radiation is contained in an amount of 0.01 to 50 parts by weight based on 100 parts by weight of (A) the polyimide precursor.
4) A positive type photosensitive resin composition as defined above, wherein R1 in the formula (1) is, in an aromatic group(s) having four bonding arms, a tetravalent group having a chemical structure of an aromatic group substituted by an aprotic electron donative group or a fluorinated alkyl group.
5) A positive type photosensitive resin composition as defined above, wherein R2 in the formula (1) is, in an aromatic group having four bonding arms or aromatic groups having bonding arms and adjacent to each other through an ether bond(s), a tetravalent group having a chemical structure of an aromatic group substituted by an aprotic electron donative group.
6) A positive type photosensitive resin composition as defined above, wherein Component (A) is a polyoxazole precursor having a structural unit represented by the following formula (2): 
wherein R5 represents a divalent organic group, R6 represents a tetravalent organic group, and each of R7s independently represents a monovalent group constituting acetal or ketal, an alkoxyalkyl group or an alkylsilyl group, which can be converted into a hydrogen atom by decomposition with an action of an acid.
7) A positive type photosensitive resin composition as defined above, wherein (B) the compound which generates an acid by irradiating radiation is contained in an amount of 0.01 to 50 parts by weight based on 100 parts by weight of (A) the polyoxazole precursor.
8) A process for producing a pattern comprising the steps of: a step of coating the positive type photosensitive resin composition as defined above on a support and drying the same, a step of subjecting to exposure, a step of developing the exposed material by using an aqueous alkaline solution and a step of subjecting to heat treatment.
9) Electronic parts which have the pattern prepared by the process as mentioned above as a surface protective film or an interlayer insulating film.